OPTICAL FIBER ARRAY COLLIMATOR APPLIED TO MULTI-LINE LiDAR

Abstract

An optical fiber array collimator is disclosed for use in a multi-line LiDAR application. The collimator includes an optical fiber array assembly, a collimating lens assembly and a housing. The optical fiber array assembly and a collimating lens assembly are positioned, assembled, and fixed in the housing. The light output surface of the optical fiber array assembly is installed near the focal plane of the collimating lens assembly. By adjusting the distance between the optical fiber array and the collimating lens, the high-precision collimated output beams from multiple optical fibers can be realized simultaneously. The fiber array can be packed and assembled with dozens or hundreds of fibers with high density. The fiber arrangement has the characteristics of adjustable density, high precision spacing and high reliability. The collimating lens includes at least one spherical or aspherical lens, which can achieve minimal aberration in different fields of view through optical design optimization. The laser spot after collimating has the characteristics of high beam quality, small wavefront distortion and small far-field divergence angle, which can achieve accurate detection of distant targets. In this collimator, due to the fiber location at vertical direction from different channels of the fiber array having different height with respect to the main optical axis of the collimating lens, the output collimating beam will have different emergence angle, which have different viewing angles. By designing and adjusting the fiber locations(height) in the fiber array with respect to the main optical axis, we can realize the accurate control of the field angle; by controlling the density and interval of the fiber distribution in optical fiber array, the density distribution of multiple collimating laser beams at different field angles can be realized. The disclosure can be widely used for multi-line LiDAR. Because the fiber is very fine, it can be assembled and arranged on the fiber array with high density, which greatly improves the density of the light spot, and then greatly improves the angular resolution of the multi-line LiDAR in vertical space. At the same time, according to the design requirements of multi-line LiDAR, by adjusting the density distribution of optical fibers on the fiber array, it can meet the differential application requirements for LiDAR in different vertical fields of view. The disclosure of the collimator has N (N≥2) optical fiber input and can be connected with 1xN optical splitter components (including fiber coupler, optical fiber splitter, optical switch, etc.), which can achieve one beam from one laser source split into N beam and then N beam are collimated, which can greatly reduce the number of laser source and cut the cost of LiDAR, and reduce the volume of the device. The disclosure has the advantages of simple overall structure, easy adjustment and assembly, small volume, easy for mass production, low cost and high reliability, which can not only meet the huge demand of the future market for LiDAR, especially multi-line LiDAR, but also meet the high standard and stringent environmental reliability requirements of the automobile industry.

1 . A collimator assembly for producing a plurality of laser beams, the collimator assembly comprising:
 a housing having an input and an output;   an optical fiber array having a plurality of optical fibers and having a connector, the plurality of optical fibers having fiber ends and being configured to emit the laser beams from the fiber ends, the connector having the fiber ends of the plurality of optical fibers arranged in an array, the connector being disposed in the input of the housing; and   a collimating lens component disposed in the output of the housing and having a focal plane near an output surface of the laser beams from the optical fiber array.   
     
     
         2 . The collimator assembly of  claim 1 , wherein the connector comprises:
 a base component having V-grooves with the fiber ends installed therein; and   a cover plate affixed to the base component to cover the fiber ends.   
     
     
         3 . The collimator assembly of  claim 2 ,
 wherein a pitch between the V-grooves has an accuracy of 0.5 microns, and   wherein spacing between the V-grooves are unevenly or evenly distributed.   
     
     
         4 . The collimator assembly of  claim 1 , wherein the plurality of optical fibers are single-mode or multi-mode optical fibers. 
     
     
         5 . The collimator assembly of  claim 1 ,
 wherein spacings between the plurality of optical fibers is unevenly distributed or evenly distributed in the optical fiber array,   wherein a distance between cores of the plurality of optical fibers range from 0.2 mm to dozens of millimeters, and   wherein an accuracy in the spacing is 0.75 micron or less.   
     
     
         6 . The collimator assembly of  claim 1 ,
 wherein the connector comprises an end face defined at an angle relative to the fiber ends, and   wherein the angle ranging from 4 degrees to 20 degrees.   
     
     
         7 . The collimator assembly of  claim 1 , wherein the connector comprises a polished face coated with an anti-reflection film having a wavelength range of 800 nm to 1600 nm. 
     
     
         8 . The collimator assembly of  claim 1 , wherein the collimating lens component comprises at least one spherical lens or aspherical glass lens. 
     
     
         9 . The collimator assembly of  claim 1 ,
 wherein the collimating lens component comprises a cemented lens component containing two or more lenses, and   wherein materials of the two or more lenses have have different refractive index values and Abbe numbers.   
     
     
         10 . The collimator assembly of  claim 1 , wherein a surface of the collimating lens component is coated with an antireflection film having a wavelength range of 800 nm to 1600 nm. 
     
     
         11 . The collimator assembly of  claim 1 , wherein the housing is composed of aluminum, aluminum alloy, stainless steel, or other alloy. 
     
     
         12 . The collimator assembly of  claim 1 , wherein a surface of the housing is treated with blackening or anodic oxidation. 
     
     
         13 . The collimator assembly of  claim 1 , wherein the optical fiber array comprises a plurality (L) of (1xN) optical fiber array elements superimposed together and forming a two-dimensional optical fiber array of LxN. 
     
     
         14 . The collimator assembly of  claim 1 , wherein the optical fiber array comprises an integrated LxN two-dimensional fiber array assembly. 
     
     
         15 . The collimator assembly of  claim 1 , comprising an optical fiber coupler or fiber splitter having at least one input port and having a plurality of output ports,
 wherein the output ports are connected to the plurality of optical fibers of the optical fiber array.   
     
     
         16 . The collimator assembly of  claim 15 , comprising a laser source connected to the at least one input port and configured to output laser transmission power,
 wherein the optical fiber coupler or the fiber splitter divides the laser transmission power of the laser source to the plurality of output ports.   
     
     
         17 . The collimator assembly of  claim 15 ,
 wherein the optical fiber coupler or the fiber splitter comprises a 1xN fiber coupler having one input end and having N outputs, and   wherein the N outputs are cascaded through a number of fiber couplers or fiber splitters.   
     
     
         18 . The collimator assembly of  claim 15 , comprising an optical switch having at least one input port and having a plurality of output ports,
 wherein the at least one input port is configured to receive laser transmission power,   wherein the plurality of output ports is connected to the plurality of optical fibers of the optical fiber array, and   wherein the optical switch is configured to switch the laser transmission power from the at least one input port between the plurality of output ports.   
     
     
         19 . A Light Detection and Ranging (LiDAR) system, comprising:
 a plurality of transmitters using one or more of a collimator assembly according to  claim 1 , the plurality of transmitters being configured to transmit a plurality of optical beams; and   a plurality of receivers being configured to receive reflected returns from the plurality of optical beams.   
     
     
         20 . A method of assembling a collimator assembly for use with a Light Detection and Ranging (LiDAR) system, the method comprising:
 attaching a connector to fiber ends of a plurality of optical fibers in an optical fiber array;   installing a collimating lens component into an output end of a housing;   locating the connector of the optical fiber array in an input end of the housing;   fine-tuning a distance and an angle between the fiber ends and the collimating lens component by monitoring wavefront distortion and dispersion angle of a collimated beam while adjusting the optical fiber array relative to the collimating lens component; and   affixing the connector of the optical fiber array to the input end at the fine-tuned distance and angle.   
     
     
         21 . The method of  claim 20 , wherein locating the connector and adjusting the optical fiber array comprise holding the optical fiber array by a vacuum fixture on a high-precision five-dimensional device. 
     
     
         22 . The method of  claim 20 , wherein fine-tuning the distance and the angle comprises fine-tuning the distance and the angle at a same time using a wavefront sensor and a beam profiler to monitor the wavefront distortion and the dispersion angle. 
     
     
         23 . The method of  claim 20 , wherein affixing the connector of the optical fiber array to the input end comprises using an ultra-violet (UV) glue. 
     
     
         24 . The method of  claim 20 , wherein attaching the connector to the fiber ends of the plurality of optical fibers in the optical fiber array comprises:
 forming a series of through-holes with sub-micron size and spacing in a glass plate or Si plate using a lithography process;   affixing the fiber ends in the through-holes;   grinding and polishing end faces of the fiber ends; and   coating the end faces with an anti-reflection film having a wavelength range of 800 nm to .1600 nm covering an emission wavelength of the LiDAR system.   
     
     
         25 . The method of  claim 20 , wherein attaching the connector to the fiber ends of the plurality of optical fibers in the optical fiber array comprises:
 placing the fiber ends in V-grooves defined in a base component;   affixing a cover on the base component over the fiber ends; and   grinding and polishing end faces of the fiber ends.   
     
     
         26 . The method of  claim 20 , wherein installing the collimating lens component into the output end of the housing comprises engaging the collimating lens component against a positioning step defined in the output end of the housing. 
     
     
         27 . The method of  claim 20 , wherein locating the connector of the optical fiber array in the input end of the housing comprises engaging the connector against a positioning step defined in the output end of the housing.